The concept of head-carrying slider units which float in near-contact against a disc surface, subject to a lift force generated by frictional air movement due to the relative movement of the slider and disc is well know. The slider units have been applied in information recording devices for use, for example, as an external memory for information processing apparatus such as computers and word processors. A recording medium used is typically a magnetic or optical disc, although other media may also be used.
A typical slider unit for carrying the reading or reproducing head, typically includes a magnetic head or optical head, formed with an air bearing structure on that side which faces the medium in use (hereinafter called the "float side"). Air passing between the float side and the medium generates a lift force on the slider unit. Usually the slider unit is mounted at the end of an arm which can exert a force towards the medium to counterbalance the lift force, to achieve a stable floating condition with a small gap (referred to hereinafter as the "flying height") between the slider unit and the medium surface.
It is generally recognized that the flying height should be maintained as small as possible, indeed approaching zero, so as to maximize the information density that can be recorded on or reproduced from the information medium. For example, the flux from a magnetic recording head diverges away from the heat so that the necessary area for one bit of information increases with increasing distance of the head from the medium. Accordingly, various proposals have been made to reduce the flying height to a distance of the order of a few tens of microns (.mu.m) or less.
The technical problems of controlling the flying height under these conditions are large. A typical slider unit may several tens of mg and must be supported at an infinitesimal spacing from a fast-moving medium, for example, a disc rotating at several thousand rpm. Furthermore, the variation of this tiny spacing must be rigorously minimized.